The Quartet of Middle East mediators has criticized Israel's move to expand settlements in the West Bank, describing it as a threat to efforts for peace between the Israelis and Palestinians.

In a joint statement, the Quartet -- the European Union, Russia, the United Nations, and the United States -- said it was "greatly concerned by Israel's recent announcements to advance planning for new housing units in Ariel and East Jerusalem."

The statement said the future of Jerusalem, in particular, is an issue that must be resolved through negotiations, and warned against any "unilateral action" by either side.

Israel on August 15 announced approval of the building of 277 new homes in the West Bank -- despite opposition to the move by its ally, the United States.

Palestinian leaders have said all new Israeli settlement activity must stop before peace talks can resume, and have threatened to present to the UN in September an application for full UN membership by a Palestinian state.